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Abstract: We evaluate post-release dispersal, growth and survival of hatchery-reared white seabass (Atractoscion nobilis) released as part of an experimental stock enhancement program in California. Releases of hatchery white seabass have been carried out since 1986, year round either directly from the hatchery or after acclimation in net pens. All released fish are implanted with coded wire tags. Post-release monitoring is carried out through a research gillnet fishery for juveniles, and tag returns from the commercial and recreational fisheries. Fish dispersed from the release sites at a diffusion rate D 795km2 year−1, such that 50% of fish remained within 47km and 95% within 135km of the release site at the end their third year at large. The von Bertalanffy growth parameters for released hatchery fish were estimated at L ∞ =975mm SL and K =0.21year−1. A set of alternative survival models accounting for dispersal and size- and time-dependent natural and fishing mortality patterns was confronted with the mark-recapture data using model selection based on the Akaike Information Criterion (AIC). The model that fit the data best accounted for short-term post-release mortality dependent on season and release method in addition to a long-term size-dependent mortality. Survival of released hatchery fish was highest in Spring, moderately lower in Summer and Autumn, but much lower in Winter releases. Acclimatisation in net pens had a substantial, positive effect on survival relative to direct releases. Survival of hatchery fish to legal minimum length (600mm SL) in the fishery was estimated at 1.5% for a release size of 200mm, rising to 13.8% for a release size of 400mm, under optimal conditions (Spring releases with net pen acclimatisation). Mortality rates of hatchery white seabass under optimal release conditions were substantially below average for other hatchery fish released into the wild, but remained above those expected for wild fish in both, the short-term and long-term components. [Copyright &y& Elsevier]

Abstract: The objective of this study was to determine the optimum dietary lipid level of white seabass, Atractoscion nobilis, which is one of the most important species in California and Baja California for sport and commercial fisheries. Triplicate groups of fish were fed for 50 days with isonitrogenous experimental diets formulated with increasing lipid levels (2.6, 7.4, 11.6, 15.3 and 19.4% lipid) using menhaden oil as the lipid source. A commercial diet (CD, 49.9% crude protein, 14.7% lipid) was also fed to triplicate groups of fish. Survival throughout the growth trial ranged from 89 to 100% but the survival of fish fed the 2.6% lipid and the commercial diet was significantly less than the rest of the diets. Final mean body weight, feed conversion ratio (FCR), and nitrogen retention efficiency (NRE: N gain/N intake) were significantly greater for diets 15.3 L and 19.4 L compared to the rest of the treatments. Daily feed intake (DFI) was variable (3.5±0.08 to 8.6±0.03) and significantly affected by dietary treatment. Lipid content of whole body, muscle and liver increased with increasing dietary lipid levels. Muscle and liver fatty acid (FA) composition reflected dietary FA profiles. Tissue n−3 and n−6 highly unsaturated fatty acids (HUFAs) content increased in direct proportion to dietary lipid levels. [Copyright &y& Elsevier]

Abstract: A study was carried out to examine the effect of lipid level on growth and feed utilization of white seabass. Fingerling white seabass (27 days old, 0.65±0.05 g, 32±3.2 mm) were fed four formulated diets with four levels of lipid (15.5%, 18%, 19.5% and 21.5% of dry matter) at one level of protein (61% crude protein, dry matter (DM) basis) for six weeks. Survival exceeded 90% for all treatments. Weight gain (g) and specific growth rate (SGR, % day−1) values indicated that fish fed diets with 15.5% and 18% lipid exhibited higher growth performance. Lowest growth was recorded for fish fed diets with 19.5% and 21.5% lipid. Feed intake (FI, g fish−1) was also significantly (P <0.001) affected by dietary lipid levels and tended to decrease with increasing lipid levels. However, the fish that showed the highest FI were those that were fed the 15.5% and 18% lipid diets. Feed conversion ratio (FCR) values indicated that diets containing 19.5% and 21.5% lipid were more efficiently utilized. No significant differences in muscle composition were observed among fish fed the different diets. However, there was a strong linear relationship (P <0.05) between dietary lipid level and liver lipid. Hepatosomatic index (HSI) increased with dietary lipid level. Results indicated that fish performed best with the diets containing 15.5% and 18% lipid when protein concentration was 61.45±0.07%. And, reduced growth and increased body fat were evident when dietary energy increased from 24.2 to 24.9 kJ g−1. More work is needed to determine the precise dietary protein and carbohydrate requirements for this profitable aquaculture species. [Copyright &y& Elsevier]

Five cohorts of cultured California Yellowtail (Seriola dorsalis) were used in exercise training experiments to assess the duration of exercise necessary to induce a positive growth and fitness response, quantify the variability and replicability of this response between cohorts, and track the longevity (persistence) of exercise-induced benefits following removal from the exercise stimulus. Custom-designed raceways were used to continuously exercise juvenile yellowtail at their optimal swimming speed for two, three, or four weeks following which several fitness metrics including measures of somatic growth, white muscle fiber area, metabolic rate, and feed conversion were tracked for up to 20 weeks post exercise in comparison to non-exercised controls. Within a cohort, the longest duration of exercise (4 weeks) generally had the largest and longest-lasting impact on growth, followed by the 3-week, and then the 2-week exercise regimes. However, all exercise treatments showed substantial variability in the magnitude and longevity of the response between cohorts. For example, the positive growth response (increase in mass above that of controls) of the 4-week swimming group ranged from 9.8% to 37.8% between cohorts. This variability in the exercise response between cohorts is similar in magnitude to that associated with other experimentally manipulated variables in the exercise regimes of previous studies, and thus highlights the need for additional species-specific experiments to quantify replicability of positive exercise results. In addition, the longevity of exercise-induced benefits was highly variable between cohorts and generally not retained for prolonged periods post exercise. Most notably, the exercise-induced growth response which may result from muscle hypertrophy (increase in white muscle fiber size) during exercise, subsided within weeks. Taken together, these results indicate that exercise can play an important role in the growth and fitness of S. dorsalis and other species, however the duration of the exercise, as well as the timing of exercise in the rearing process likely have important implications for optimizing exercise training for aquaculture enhancement. • Increased exercise duration leads to increased growth and physiological benefits. • The magnitude of the growth response to exercise is highly variable between cohorts. • Exercise-induced physiological benefits diminish quickly post-exercise. [ABSTRACT FROM AUTHOR]